A device for the semiautonomous support of a parking process for vehicles is described in German Patent Application No. DE 10 2005 008 176 A1.
In contrast to fully autonomous devices for the support of parking processes, in the case of semiautonomous devices, that is devices which make available support power semiautonomously during the parking of vehicles, the cooperation of a driver is relied upon. In the case of devices for semiautonomous support of a parking process, the driver generally at least either accelerates and brakes, or intervenes in the parking process by steering. In contrast to these devices that operate semiautonomously, in the case of fully autonomous devices, that is, devices which put together fully autonomous support power during the parking process, neither steering not braking and/or giving gas is expected of the driver.
Furthermore, in the case of devices which autonomously support the parking process of vehicles, intervention is only conditionally possible.
Devices for the semiautonomous support of a parking process are used in land-bound vehicles, especially in motor vehicles equipped with an internal combustion engine, such as passenger cars.
German Patent Application No. DE 10 2005 008 176 A1 describes an arrangement for automatic steering that superposes steering torque on the steering wheel of the vehicle that is to be parked. If the steering torque is greater than the frictional forces between tires and roadway, the vehicle is automatically steered. However, the driver controls the steering wheel motion of the vehicle independently. The device described in German Patent Application No. DE 10 2005 008 176 A1 for the semiautonomous support of a parking process does not intervene independently in the control of the steering wheel motion of the vehicle. However, using sensors mounted on the outside of the vehicle, it measures the parking space and also ascertains a desired entry trajectory. The entry trajectory is the curve that is covered optimally by the vehicle during parking.
German Patent Application No. DE 10 2005 008 176 A1 also describes an arrangement held in reserve which ascertains the maximum possible steering speed. It also describes that an arrangement is held in reserve which determines the steering speed, that is, the speed for the application of steering torque to a steering wheel and/or a steering shaft via appropriate assemblies. In this context, an adjustment is produced in a computing device between the calculated steering speed and the maximum possible steering speed. If the calculated steering speed is greater than the maximum possible steering speed which is able to apply the means for automatic steering, either an instruction is output to the driver to lower the speed, or the speed is automatically reduced via a limiting device.
If, during parking of the vehicle and being aided by the semiautonomously working device, the driver does not operate the steering wheel, the steering torque required for controlling the steering wheel is applied exclusively by a steering device, that is, a steering actuator device, such as an electric motor. Such electric motors are part of appropriate steering devices that are also known as EPS, i.e., electronic power steering.
However, for large steering angles, large steering torque generally has to be applied, particularly when the vehicle to be parked is at a standstill. High currents are then required of the steering device, which may amount, at times, up to 100 Amps. In such high-load situations, diverse problems appear in the conventional devices. For instance, the conventional devices are not able to park the vehicle that is to be parked in one reverse move, but require at least one additional forward move. This problem occurs particularly in small parking spaces. In such cases, if one wants to achieve a low longitudinal distance from a lateral limitation, such as a curb, each change in direction is accompanied by a maximum steering angle. To be sure, in a case like that the vehicle is usually standing still, while the steering device is instructed to execute a maximum steering angle.
Mechanical steering systems used up to now have unfavorable force transmission, particularly in the case of large steering angles, so that particularly large steering torques have to be applied if a maximum steering angle is to be achieved.
The problems are aggravated if the pavement, on which the vehicle is located, and/or the tire quality used by the vehicle displays a particularly firm grip. It then sometimes becomes possible only to achieve a partial steering angle.
The problem is further aggravated if the battery supplying the steering device with current is weak, or if a steering assembly of the steering device detects a high thermal load, whereby the maximum deliverable steering torque is reduced. Even in such cases, the desired steering angle can no longer be fully implemented.
The maximum steering angle that can be achieved is therefore greatly different, even within a single parking process, and is not predictable in all cases.